Why a Swept-Wing?

On Sun, 11 Jan 2004 18:20:34 GMT, Ed Rasimus
wrote:

As I recall the X-29 project, one of the objectives was evaluation of
the instability as a means of gaining agility for future highly
maneuverable aircraft. The "urban legend" was that the aircraft
required minimum of triple redundant FBW augmentation as loss of the
augmentation would result in immediate excursions from stable flight
and structural failure within seconds. The ultimate in "JC maneuvers".

Well, it didn't have to have all three computers working, just one,
which could have been the fourth, back-up one. But that wasn't a
long-term sort of thing.

However, it didn't hang around for seconds before it pitched up.
stalled, and departed controlled flight. Time to double amplitude was
a small fraction of a second, although I can't remember the number.
It was smaller than that of the F-16, but the F-16 isn't very unstable
(it's neutrally stable clean and full of fuel and could be flown,
albeit rather oddly, without augmentation until enough fuel burned
off, not that anyone except VISTA would try this).

The X-29 was statically unstable because the project was a technology
demonstrator for agile aircraft with forward-swept wings, aircraft
that were stall-resistant. It wasn't statically unstable because it
had a forward-swept wing.

Always thought it made for an extremely ugly airplane.

I thought it wasn't all that bad looking, myself. The X-31 was rather
plain, but the X-29 was OK.

Wasn't the basic structure from an F-16A?

No, that was the X-31, I think, at least for the gear and cockpit.
The X-29 used a couple of F-5s for the fuselages. I don't remember
how far aft the F-5 airframe went, but it definitely included the
cockpit and surrounding structure, as well as the gear, as I recall.

Mary

--
Mary Shafer Retired aerospace research engineer

"Mary Shafer" wrote in message
...

snip
However, it didn't hang around for seconds before it pitched up.
stalled, and departed controlled flight. Time to double amplitude was
a small fraction of a second, although I can't remember the number.
It was smaller than that of the F-16, but the F-16 isn't very unstable
(it's neutrally stable clean and full of fuel and could be flown,

This is closer than Mary's claim that the F-16 is statically unstable, but
the F-16 continues to remain 5% pitch stable.

Uzytkownik "Alan Dicey"
napisal w wiadomosci ...
As far as I can recall, forward sweep confers the advantage that
spanwise flow is now inwards, and the wingtips (with associated control
surfaces) stall last instead of first, so control authority is retained
at higher angles of attack or "deeper into the stall". In the X-29 they
were combined with canards, a supercritical wing and aerodynamic
instabilty in a search for enhanced maneuverability. See here

http://www.dfrc.nasa.gov/Newsroom/Fa...-008-DFRC.html

for the NASA Dryden infosheet. I seem to remember that the advantages
gained did not warrant the construction costs/difficulties (aeroelastic
tailoring with composites in the wing structure, as I recall) and so the
technique was not carried forward into new fighter design. Perhaps Mary
Shafer may know more of the projects findings?


I dug through my old notices on X-29A and X-31X and found these references:
[1] Bandyopadhyay G. - "Low-Speed Aerodynamic Characteristics of
Close-Coupled Canard Configuration at Incidence and Sideslip", Journal of
Aircraft, Vol. 28, No. 10, October 1991
[2] Er-El J. - "Effect of Wing/Canard Interference on the Loading of a Delta
Wing", Journal of Aircraft, Vol. 25, No. 1, January 1988
[3] Manoeuvring Aerodynamics, AGARD CP 497, Toulouse, France, May 1991
(especially papers)
[3.a] Ross Hannes - "X-31 Enhancement of Aerodynamics for Maneuvering beyond
Stall", Paper 2
[3.b] Kraus W. - "X-31, Discussion of Steady State and Rotary Derivatives",
Paper 13
[3.c] Ferretti A., Bartoli A., Salvatore A. - "Prediction of Aerodynamic
Phenomena Limiting Aircraft Manoeuvrability", Paper 5
[3.d] Visintini L., Pertile R., Mentasti A. - "Parametric Effects of some
Aircraft Components on High-Alpha Aerodynamic Characteristics", Paper 6

Close-Coupled Canard was my main area of interest these days so sweep
(-forward or -back) can be treated mariginally in these papers, but I hope
they can help you.

Regards
JasiekS
Warsaw, Poland

"JasiekS" wrote in message
...

Close-Coupled Canard was my main area of interest these days so sweep
(-forward or -back) can be treated mariginally in these papers, but I hope
they can help you.

The major interesting fearure of the X-29 was the two poles in the right
half of the s-plane.

Two poles in the right half s plane made it inherently unstable, right?

Does that mean LOT, the Polish airlines, can have seats only on the lefthand
side of their airplanes.

WDA

end

"Tarver Engineering" wrote in message
...

"JasiekS" wrote in message
...

Close-Coupled Canard was my main area of interest these days so sweep
(-forward or -back) can be treated mariginally in these papers, but I
hope
they can help you.

The major interesting fearure of the X-29 was the two poles in the right
half of the s-plane.

"W. D. Allen Sr." wrote in message
...
Two poles in the right half s plane made it inherently unstable, right?

Pitch unstable, but the poles being complex in nature eliminates most folks
(including aero engineers) from the discussion.

Does that mean LOT, the Polish airlines, can have seats only on the
lefthand
side of their airplanes.

No.

On Fri, 23 Jan 2004 10:34:23 -0800, "W. D. Allen Sr."
wrote:

Two poles in the right half s plane made it inherently unstable, right?

Does that mean LOT, the Polish airlines, can have seats only on the lefthand
side of their airplanes.

Engineering humor... LOL.

--
__________ ____---____ Marco Antonio Checa Funcke
\_________D /-/---_----' Santiago de Surco, Lima, Peru
_H__/_/ http://machf.tripod.com
'-_____|(

remove the "no_me_j." and "sons.of." parts before replying

Originally Posted by James Dandy

Pardon my ignorance on all matters concerning modern aviation but just
why the hell would you want to sweep a wing forward?

Doesn't that make any aircraft unstable? If so, why would any pilot
feel safe in it?

Has anyone ever made one work?

James Dandy

Swept-wing spread - low speed and manouverability.
Unspread - higher speed and intercepting